Mobile radio communication system

ABSTRACT

A mobile radio communication system operating between a moving train and a stationary land station comprises a leaky waveguide or the like which is partly opened by providing a plurality of perforations or slits and a controlling device distributed along the waveguide or the like so that the electromagnetic wave transmitted in the waveguide leaks out of the waveguide only at that portion where the train is progressing. The controlling device may comprise a metallic cover to open or close the perforations or slits or matching elements which may vary the leakage impedance through the perforations or slits upon detection of the approaching train.

Inventors Tsunco Nakahara Nlshinonlya-shi;

Hiroshl Kitani, Higashl, both of, Japan Appl. No. 776,100 Filed Nov. 15, 1968 Patented July 13, 1971 Assignec Sumitaao Electric Industries, Ltd.

. Osaka, Japan Priority Nov. 17,1967

Japan 42/73977, 42/73979 and 42/73980 MOBILE RADIO COMMUNICATION SYSTEM 52, 53, 54, 117,125, 308, 140; 340/258, 258 C; 246/187, 187 C; 343/71 l, 713, 767, 768-70, 6.5, 13; 333/12, 84, 95; 179/25, 82

[56] References Cited UNITED STATES PATENTS 2,605,413 7/1952 Alvarez 343/768 X 2,921,979 1/1960 l-lafner l79/2.5 3,175,218 3/1965 Goebels, Jr 343/770 X 3,204,242 8/1965 Goebels, Jr 343/768 3,278,850 10/1966 Tomizawa et al.. 325/52 3,466,651 9/1969 Bigelow 343/6.5

Primary Examiner-Benedict V. Safourek Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT: A mobile radio communication system operating between a moving train and a stationary land station comprises a leaky waveguide or the like which is partlyopened by providing a plurality of perforations or slits and a controlling device distributed along the waveguide or the like so that the electromagnetic wave transmitted in the waveguide leaks out of the waveguide only at that portion where the train is progressing. The controlling device may comprise a metallic cover to open or close the perforations or slits or matching elements which may vary the leakage impedance through the perforations or slits upon detection of the approaching train.

PATENTED JUL 1 3 I97! SHEET 1 BF 3 FIG. I

FIG. 2

FIG. 4

FIG. 3

ATTOR N E Y5 PATENTED JUL] 31971 3,593,143

SHEET 2 0F 3 I NVEN TOR S.

TSUNEO NAKAHARA HIROSHI KITANI ATTORNEY PATENTEU JULI 319m 3593143 SHEET 3 {1F 3 FIG. I20 FIG. |2b

I NVEN TOR 5.

TS UNEO NAKAHARA HlROSHl KITANI ATTORNEYS.

MOBILE RADIO COMMUNICATION SYSTEM BACKGROUND OF THE INVENTION This invention relates to a mobile radio communication system to be used between a railroad train and a stationary land station.

Heretofore, for the purpose of obtaining a suitable radio communication system between a moving train and a stationary land station, intense studies have been carried out on systems wherein a leaky or perforated waveguide is installed along the railroad so that an electromagnetic wave is emitted along the railroad with an antenna provided on the train for receiving the emitted electromagnetic wave. However, in such a conventional system, the electromagnetic wave is incessantly radiated from the leaky waveguide along its entire length, and on the other hand, the antenna provided on the train is merely of a length of several meters. For this reason, the receiving efficiency in conventional radio communication systems for the transmitted electromagnetic wave is extremely low, ranging among -60 and 80 db. In addition, because of the significant loss due to the leakage electromagnetic wave, the number of the repeaters (or relaying units) installed along the leaky waveguide must be increased at shorter intervals. This causes drawbacks in the conventional mobile radio communication systems such as an increase in the installation cost, difficulties in the maintenance, and reduced reliability of operation.

SUMMARY OF THE INVENTION Therefore, the primary object of the present invention resides in eliminating the above-described drawbacks of conventional mobile radio communication systems.

According to the present invention, the leaky waveguide is provided with a controlling device distributed along the entire length of the waveguide, and merely those controlling elements located in the nearest portion of the waveguide to the moving train are allowed to leak out the electromagnetic wave from the waveguide and the transmission loss of the waveguide is remarkably decreased.

BRIEF DESCRIPTION OF DRAWINGS For the purpose of better understanding of the present invention, a number of embodiments thereof will now be described in connection with the accompanying drawings, in which:

FIG. I is a schematic plan view showing the principle of the mobile radio communication system according to the present invention;

FIG. 2 is a perspective view ofa part of the leaky waveguide constituting an embodiment of this invention;

FIGS. 3 and 4 are crosssectional views showing different states of operation of the embodiment illustrated in FIG. 2;

FIGS. 5 and 6 are cross-sectional views showing different states of operation of another embodiment of the present invention;

FIG. 7 is a perspective view, partially in section, ofa part of another type of the waveguide wherein matching elements are utilized; and

FIGS. 8 through lll, 12a and 12b are cross-sectional views of various embodiments wherein different types of matching elements are employed.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. I, there is illustrated a train 3 running on a railroad I, along which a leaky waveguide 2 is installed. The principal feature of the present invention resides in that only a portion 5 within the entire length of the leaky waveguide 2, which is in the vicinity of the running train 3, is allowed to leak a part of the electromagnetic wave transmitted through the waveguide 2 into the surrounding atmosphere, and that the remaining portions of the waveguide are prohibited from leaking out the electromagnetic wave.

FIG. 2 illustrates an embodiment of the present invention whereby the above-described feature is realized. In this drawing, a leaky waveguide 22, consisting of a metal tube such as aluminum, is provided with a series of leakage perforations or slits 6, equidistantly distributed along the length of the waveguide 2. Supposing that a radio wave (electromagnetic wave) of, for instance, TE mode is transmitted in the waveguide 2, the wall current on the inside surface of the waveguide 2 is interrupted by the existence of perforations of slits 6 thereby allowing a part of the radio wave to leak out of the waveguide 2 through the perforations or slits 6. The leakage of the radio wave can be blocked by means of a cover or a reflecting plate 7 which opens or closes the perforations or slits 6 through the operation of an electric motor 9 and driving link 8.

FIG. 3 illustrates the state of operation wherein the electric motor 9 mounted on a support 10 is not energized and the reflecting plate 7 is contacting on the leaky waveguide 2 so that the leakage perforations or slits 6 are closed by the reflecting plate 7 and the leakage of the radio wave is thereby interrupted.

FIG. 4 illustrates another state of operation wherein the electric motor 9 is energized and the reflecting plate 7 is raised upwards by means of the driving link 8. In this state, the leakage of the radio wave is allowed through the perforations or slits 6 for radiation into the outside atmosphere. Switching means (not shown) for the electric motor 9 is automatically operated by a detector (not shown) which sense the approach of the running train. The det; :tion of the approaching train can be exercised by several methods such as utilizing the variation of the current flowing through the rails or by a loop installed under the rails or mechanically by detecting the variation of weight supported by the rails.

Although in the above description, the leaky waveguide is stationary and the reflecting plate is moved in the vertical direction, it is also possible that the leaky waveguide may be rotated about its longitudinal axis and the leakage perforations or slits are thereby open or closed. FIGS. 5 and 6 illustrate an embodiment having such construction. In this embodiment, the rotatable waveguide 11 is shown to have two rows of perforations or slits 6' for the purpose of radiating the electromagnetic wave in two directions. On this waveguide, a stationary reflecting plate 12 having semicircular sectional configuration is provided, and the waveguide is rotated about its lo.. .:udinal axis between the opened position shown in FIG. 5 and the closed position therefrom, as shown in FIG. 6 where the leakage of the electromagnetic wave is blocked and reflected back into the waveguide, The rotation of the waveguide may be exercised by outside means not shown which is controlled by the detecting device (not shown) for the approaching train as described above in conjunction of FIG. 4.

In the above description, although embodiments wherein the leakage perforations or slits of the waveguide are open or closed mechanically have been depicted, it is also possible that these functions may be carried out electrically. In such cases, there are utilized impedance matching devices provided along the leaky waveguide, and the leakage impedance of the waveguide portion near the moving train is brought into matching condition so that the radio wave transmitted through the waveguide is partly leaked out of this portion of the waveguide into the atmosphere. In this case, however, the matching devices at the other portions of the waveguide are left in the not-matching state, and the electromagnetic wave is not radiated from these portions of the waveguide.

FIG. 7 illustrates a typical construction of the waveguide wherein a leakage waveguide 2' made of a metal such as aluminum is provided with a row of leakage perforations or slits 6" and also a support 13 on which a matching element (not shown) of desired type will be mounted. When the matching element mounted on the support 13 is brought into the matching condition under the control of a detecting device (not shown) which senses the approach of the running train, the wall impedance seen from the inside to the outside of the waveguide through the perforations or slits 6" is so adjusted that the radio wave transmitted in the waveguide may be leaked out of the perforations or slits 6". However, if the matching element is not brought into the matching condition, as in the case of the rest ofthe portions of the leaky waveguide remote from the train, the leakage of the radio wave through the perforations or slits 6" is substantially eliminated.

In FIGS. 8 through 12, various embodiments of the present invention are illustrated wherein different kinds of matching elements are mounted on the support 13. In these drawings, the leaky waveguide 2 is made of a metal tube of, for instance, aluminum or copper plated steel, and a row ofleakage perforations or slits 6" are bored through the wall of the waveguide 2. Supposing that a TE mode electromagnetic wave is transmitted through the waveguide 2, a current flowing along the inside surface of the waveguide 2 is interrupted by the leakage perforations or slits 6, and a part of the electromagnetic wave leaks out ofthe waveguide 2.

FIG. 8 is an embodiment where a varactor diode is mounted inside of the support I3. The varactor diode 14 can vary its impedance depending upon the bias voltage, whereby the matching impedance of a waveguide portion can be adjusted so that the wall impedance looking outside of the waveguide may be brought into matching condition upon the approach of the moving train. When the train passes by, the bias voltage for the varactor diode 14 is varied, and the reactance of the diode is converted, for instance, from inductive to capacitive or vice versa. As a result, the wall impedance is varied from the matching condition and the electromagnetic wave is prevented from leaking out of the waveguide. The approach or receding of the moving train can be detected, for instance, by sensing the current flowing through the railroad, or by variation in inductance ofloops buried under the railroad, and the bias voltage to be applied on the varactor diode 14 may be changed depending on the result of such detection.

FIG. 9 illustrates another case where a dielectric substance 15 is employed as the matching element which is distributed continuously or intermittently along the length of the waveguide 2'. When this dielectric element 15 is displaced toward or away from the leakage perforations or slits 6" by means of an electric motor 16 and an intermediate link 17, the matching condition of the leakage impedance can be obtained.

FIG. illustrates still another embodiment where a magnetic substance 18 such as ferrite is employed for the matching element which is distributed continuously or intermittently along the length of the waveguide 2. The magnetic element 18 is also displaced toward or away from the leakage perforations or slits 6" as in the case of FIG. 9. The operation of the magnetic element is similar to the dielectric element except that the nature of the reactance is inductive instead of capacitive.

FIG. 11 illustrates further embodiment of the present invention where a metallic substance is utilized as the matching element l9 distributed continuously or intermittently along the length of the waveguide. In operation, the metallic element is displaced toward or away from the leakage perforations or slits 6" as in the cases of FIGS. 9 and 10, and the impedance characteristic is varied depending on the size of the metallic element.

FIG. 12a and 12b illustrates still further embodiment, where a metallic substance is employed for the matching element. However, the metallic substance in this case is made of a metallic cylinder 20 and a metallic piston 21, and a leakage perforation or slit 22 extends through the metallic cylinder 20. In this embodiment, when the metallic piston 21 is driven to the right hand extremity, as shown in FIG. 12b, by means of driving electric motor 16 and intermediate link 17, the waveguide 2 is brought into the matching condition, and a part of the electromagnetic wave passing inside of the waveguide 2 leaks out of the coupling hole 6" and the leakage perforation or slit 22. When the train passes by, the metallic piston 21 is driven to the leftward extremity as shown in FIG.

12a, and the waveguide 2 is brought into the nonleakage condition. In this case too, the leakage impedance when seen from inside to outside of the waveguide is altered by the position of the metallic piston 21, whereby the leakage of the electromagnetic wave is controlled depending on the existence of the running train in the vicinity ofthe waveguide portion.

As described above, according to the present invention, the electromagnetic wave transmitted along the leaky waveguide or the like is allowed to leak out at a portion where the moving train is approaching, and leakage is not allowed along the rest of the portions remote from the train. As a result, the electromagnetic wave may be radiated concentratedly near the antenna of the running train with a resultant stronger field. This makes it possible to reduce the power of the transmitter, and because of the reduced transmission loss of the waveguide, the size of the leaky waveguide may also be reduced. Furthermore, the elimination of the leakage electromagnetic wave over the rest portions of the waveguide can promote the possibility of approval of its installation even in districts where local radio wave regulation is strict.

In the above description, although the invention has been described in connection with leaky waveguide, it will be apparent to those skilled in the art that the invention is not limited to the waveguide only, but it is applicable to all ofopen type lines such as a leaky coaxial line which is coaxial cable provided with leakage perforations or slits.

We claim:

1. In a mobile radio communications system for a moving vehicle traveling a predescribed route including a leaky waveguide having a series of longitudinally spaced leakage perforations extending along said route and antenna means carried by said vehicle and operatively disposed with respect to said waveguide, the improvement comprising:

a plurality of individually movable covers disposed along said waveguide to cover respective perforations and means responsive to the movement of said vehicle relative to said waveguide to sequentially remove said covers in the immediate vicinity of said moving vehicle to allow wave transmission between the uncovered portion of said waveguide and said vehicle carried antenna means.

2. In a mobile radio communications system for a moving vehicle traveling a predescribed route including a leaky waveguide having a series of longitudinally spaced leakage perforations extending along said route and antenna means carried by said vehicle and operatively disposed with respect to said waveguide, the improvement comprising:

supporting means constituting a channel for the leaked electromagnetic wave energy, and

variable impedance means carried by said supporting means for normally mismatching the impedance between portions of said system wave communication path to prevent leakage of wave energy between said waveguide and said moving vehicle antenna,

and means for changing said variable impedance means in the immediate vicinity of said moving train to effect matching of the impedance at localized positions along said waveguide.

3. The mobile radio communications system as claimed in claim 2, wherein said variable impedance means comprises a varactor diode mounted interiorly of said supporting means and said means for operatively changing the impedance of said diode to match the impedance of a perforation viewed from the inside of said waveguide to the space impedance between said waveguide and said antenna, whereby wave energy is transmitted between the waveguide and the antenna means in the immediate vicinity of the moving vehicle.

4. The mobile radio communications system as claimed in claim 2, wherein said variable impedance means comprises a dielectric material block which is positioned in path of the wave within said supporting means, and wherein said means for changing the impedance thereof comprises means for changing the position of said dielectric material block to match the impedance of the perforation viewed from inside nel and means for changing the position of said magnetic material block to match the impedance of said perforation viewed from inside said waveguide to the space impedance between said waveguide and said moving vehicle antenna which leaks the wave energy in the immediate vicinity of the moving vehicle. 

1. In a mobile radio communications system for a moving vehicle traveling a predescribed route including a leaky waveguide having a series of longitudinally spaced leakage perforations extending along said route and antenna means carried by said vehicle and operatively disposed with respect to said waveguide, the improvement comprising: a plurality of individually movable covers disposed along said waveguide to cover respective perforations and means responsive to the movement of said vehicle relative to said waveguide to sequentially remove said covers in the immediate vicinity of said moving vehicle to allow wave transmission between the uncovered portion of said waveguide and said vehicle carried antenna means.
 2. In a mobile radio communications system for a moving vehicle traveling a predescribed route including a leaky waveguide having a series of longitudinally spaced leakage perforations extending along said route and antenna means carried by said vehicle and operatively disposed with respect to said waveguide, the improvement comprising: supporting means constituting a channel for the leaked electromagnetic wave energy, and variable impedance means carried by said supporting means for normally mismatching the impedance between portions of said system wave communication path to prevent leakage of wave energy between said waveguide and said moving vehicle antenna, and means for changing said variable impedance means in the immediate vicinity of said moving train to effect matching of the impedance at localized positions along said waveguide.
 3. The mobile radio communications system as claimed in claim 2, wherein said variable impedance means comprises a varactor diode mounted interiorly of said supporting means and said means for operatively changing the impedance of said diode to match the impedance of a perforation viewed from the inside of said waveguide to the space impedance between said waveguide and said antenna, whereby wave energy is transmitted between the waveguide and the antenna means in the immediate vicinity of the moving vehicle.
 4. The mobile radio communications system as claimed in claim 2, wherein said variable impedance means comprises a dielectric material block which is positioned in path of the wave within said supporting means, and wherein said means for changing the impedance thereof comprises means for changing the position of said dielectric material block to match the impedance of the perforation viewed from inside said waveguide to the space impedance between said moving vehicle antenna and said waveguide which leaks wave energy in the immediate vicinity of said moving vehicle.
 5. The mobile radio communications system as claimed in claim 2, wherein said variable impedance means consists of a magnetic material block having inductive properties positioned in the path of the wave energy within said supporting means so as to effectively change the impedance of said channel and means for changing the position of said magnetic material block to match the impedance of said perforation viewed from inside said waveguide to the space impedance between said waveguide and said moving vehicle antenna which leaks the wave energy in the immediate vicinity of the moving vehicle. 